As known in the art, internal combustion engines operate, in part, through the controlled actuation of engine valves. For example, for each cylinder in an internal combustion engine, there are typically at least one intake engine valve and at least one exhaust engine valve. When an internal combustion engine is operating to produce power, the engine valves are actuated in accordance with so-called (and well-known) main valve actuation motions. Additionally, the engine valves may be actuated in accordance with so-called auxiliary valve actuation motions, which may be used instead of or in addition to the main valve actuation motions, so as to modify operation of the internal combustion engine.
For example, such auxiliary valve actuation motions may be used to achieve compression release braking, or engine braking. As known in the art, compression release braking converts an internal combustion engine from a power generating unit into a power consuming air compressor through selective control of various engine valves, particularly exhaust valves. Generally, the exhaust valve(s) for a given cylinder actuated by a rocker arm that, in turn, is often operatively connected to a single exhaust valve or a plurality of exhaust valves by way of a valve bridge.
An example of such a prior art system 100 is schematically illustrated in FIG. 1. In particular, the system 100 comprises a main valve actuation motion source 102 used to actuate (or provide motions to) engine valves 104, 106 via a main motion load path or valve train 106 (which may include a valve bridge 110 in the illustrated embodiment). Similarly, the system 100 comprises an auxiliary valve actuation motion source 112 used to actuation the engine valves 104, 106 via an auxiliary motion load path or valve train 114 (which may also include a bridge pin 116 in the illustrated embodiment). Though FIG. 1 illustrates two engine valves 104,106, it is understood that this is not a requirement as a single engine valve of a given type (i.e., intake or exhaust) may be equally employed.
As used herein, the valve actuation motion sources 102, 112 may comprise any components that dictate the motions to be applied to an engine valve including hydraulic, electric, pneumatic or mechanical components, e.g., cams, electronically-controlled actuators, etc. Conversely, the motion load paths or valve trains 108, 114 may comprise any one or more components deployed between a motion source and an engine valve and used to convey motions provided by the motion source to the engine valve, e.g., tappets, rocker arms, pushrods, valve bridges, automatic lash adjusters, lost motion components, etc. Furthermore, as used herein, the descriptor “main” or “primary” refers to features of the instant disclosure concerning so-called main event engine valve motions, i.e., valve motions used during positive power generation, whereas the descriptor “auxiliary” refers to features of the instant disclosure concerning auxiliary engine valve motions, i.e., valve motions used during engine operation other than conventional positive power generation (such as, but not limited to, compression release braking, bleeder braking, cylinder decompression, brake gas recirculation (BGR), etc.) or in addition to conventional positive power generation (such as, but not limited to, internal exhaust gas recirculation (IEGR), variable valve actuations (VVA), Miller/Atkinson cycle, swirl control, etc.).
FIG. 1 also illustrates a lost motion component 118 within the auxiliary motion load path 114. As known in the art, the lost motion component 118 is a mechanism that, in a first state, maintains lash or clearance 120 between the auxiliary valve actuation motion source 112 and a component in the auxiliary motion load path 114, or between components within the auxiliary motion load path 114, such that valve actuation motions supplied by the auxiliary valve actuation motion source 112 are not transferred via the auxiliary motion load path 114, i.e., they are “lost.” For ease of illustration, the lash 120 provided by the lost motion component 118 is illustrated between the auxiliary motion load path 114 and, in the illustrated example, the bridge pin 116. However, it is again noted that this lash 120 may be provided between other components as noted above. Conversely, in a second state, the lost motion component 118 takes up the lash 120 such that the valve actuation motions supplied by the auxiliary valve actuation motion source 112 are transferred via the auxiliary motion load path 114 to the engine valve(s) 104, 106. As known in the an, the lost motion component 118 is often implemented as a hydraulically-actuated device, an example of which is illustrated in FIGS. 3 and 4. In the example of FIGS. 3 and 4, the auxiliary valve actuation motion source 112, is implemented as a rotating cam, as known in the art. Further, the lost motion component 118 is implemented in the form of a piston 302 slidably disposed within a bore housing 304. Further still, a bias spring 306 is provided between the piston 302 and bore housing 304 such that it maintains the lash space 120 between the piston 302 and the cam 112. As shown in FIG. 4, application of hydraulic pressure to the opposite face of the piston 302 (via a hydraulic, channel not shown) causes the piston 302 to extend from the bore 304, thereby taking up the lash space 120 and bringing the piston 302 into contact with the cam 112. By hydraulically locking the hydraulic fluid actuating the piston 302 (using, for example, a control valve as known in the art) the motions supplied by the cam 112 may be transferred via the piston 302.
As further shown in FIG. 1, either or both of the main load path 108 and the auxiliary load path 114 may comprise an optional automatic lash adjuster 122, 124, which may be desirable to avoid the requirement to set lash normally used to account for thermal expansion and/or component wear. As used herein, an automatic lash adjuster may be included within a motion load path to the extent that it is used to take up lash in the motion load path, and operates either directly within, or parallel to, the motion load path.
Finally, FIG. 1 also illustrates the possibility that auxiliary valve actuation motion source 112′ and auxiliary motion load path 114′ may be placed in series with, rather than in parallel to, the main motion load path 108. That is, the some or all of the main motion load path 108 may be used as part of the auxiliary motion load path 114′, as known in the art. Once again, in this embodiment, the lash 120′ provided by the lost motion component 124′ is schematically illustrated between the auxiliary motion load path 114′ and the main motion load path 108.
A problem with systems 100 of the type illustrated in FIG. 1, i.e., having separately implemented main and auxiliary valve actuation motion sources 102, 112 in combination with components capable of taking up lash space, i.e., lost motion components 118 and/or automatic lash adjusters 124, is the potential for those components to over-extend or “pump up” when not intended or desired. If such over extension (sometimes referred to as “jacking”) occurs, the motion load path in which such a component is deployed may effectively prevent proper seating of an engine valve, thereby resulting in poor performance and/or emissions and, in some instances, catastrophic valve-to-piston impact.
An example of this is illustrated with further reference to FIGS. 1, 2 and 5-7. In particular, FIG. 2 illustrates a main valve lift curve 202 and an auxiliary valve lift curve 208 for an exhaust valve that illustrate examples of valve actuation motions that may be caused by respective ones of the main and auxiliary valve actuation motion sources 102, 112. In the illustrated examples, the main lift curve 202 comprises a base circle portion 204 in which no lift is provided, as well as a main lift event 206, whereas the auxiliary lift curve 208 comprises a base circle portion 210, a BGR lift event 212 and a compression-release lift event 214. Note that the non-zero lifts in each curve 202, 208 are complementary to each other in that they do not overlap and yet provide the complete set of motions to be applied to the valve. As shown, the curves 202, 208 illustrated in FIG. 2 assume that the lost motion component 118 is currently in a state where the auxiliary valve lifts 208 are lost, as illustrated by the lash 120 such that that the auxiliary lift events 212, 214 are “below” the base circle portion 204 of the main valve lifts 202. Note that the lash 120 is greater than the maximum lift event provided by the auxiliary lift curve 208. This is further schematically illustrated in FIG. 1 by the lack of connection between the auxiliary motion load path 114 and the bridge pin 116, i.e., no valve actuation motions are conveyed by the auxiliary motion load path 114 to the bridge pin 116. Consequently, only the main lift event 206 is conveyed to bridge 110.
When the lost motion component is configured to take up the lash 120, as illustrated in FIG. 6 (in which the lost motion component 118 and optional automatic lash adjusters 122, 124 are not shown for ease of illustration), the lift curves 202, 208 are as shown in FIGS. 7 and 9, in which both the main and auxiliary valve actuation motions are conveyed to the engine valves 104, 106. Thus, for example, at time t1 shown in FIG. 7, the auxiliary motion load path 114 conveys those valve actuation motions that result in the compression-release valve event 214 being applied the bridge pin 116 and the engine valve 104. Note that, at time t1, the main valve lift curve is at its zero lift portion indicating that the main motion load path is not applying any lift to the valve bridge 110.
However, as shown in FIG. 9, at time t2, the opposite is true; i.e., the main valve lift curve is at its main lift event 206 whereas the auxiliary valve lift curve is at its zero lift point. In this case, as shown in FIG. 8, when the main motion load path 108 is applying a high lift to the valve bridge 110 and the auxiliary motion load path 108 is applying none, a lash 802 based on the height of the main lift event 206 will develop between the auxiliary motion load path 114 and, in this example, the bridge pin 116. In this case, the lost motion component 118 (not shown in FIG. 8) may attempt to take up this additional lash 802 as illustrated by the dashed arrow connecting to the bridge pin 116. This is further illustrated in the example of FIG. 5, in which the piston 302 will, under the applied hydraulic pressure, attempt to take up the additional lash 802. Consequently, at time t3 shown in FIG. 9, when the main lift event 206 has concluded, and both valve lift curves are at their respective zero lift portions, the lost motion component 118 will remain in its pumped-up or over-extended state, thereby possibly preventing complete closure of the engine valve 104.
This same problem may result where the auxiliary motion load path 114 includes the automatic lash adjuster 124 instead of or in addition to the lost motion component 118, as described above.
In order to prevent such jacking, the lost motion component 118 (and/or automatic lash adjuster 124) can be designed with a stroke limiter that prevent extension beyond a certain limit. However, this necessarily complicates the design and increases the cost of these components. Still other solutions, such as that described in U.S. Pat. No. 9,200,541, provide relatively complex piston designs that absorb certain motions while permitting other motions to be conveyed. Again, however, this increases design complexity and cost.
Thus, it would be advantageous to provide systems that address these shortcomings of existing systems.